Tokkai Hei 2-153249 published by the Japanese Patent Office in 1990 discloses an engine cylinder block for a water-cooled engine wherein a water jacket is formed around a cylinder wall, and the heat of the cylinder wall is absorbed by circulating cooling water in this water jacket.
In one kind of cylinder block, the bottom wall of the water jacket is connected to an intermediate part of the cylinder wall, and the water jacket is formed only around the upper part of the cylinder wall. In this way excessive cooling of the cylinder wall is prevented, warm up is promoted, and exhaust performance and heater performance are improved.
In an engine having a cylinder head fitted to the upper end of the cylinder block by head bolts, when the water jacket bottom wall is connected to the intermediate part of cylinder wall, an axial force which acts on the head bolts due to tightening of the head bolts or input of combustion pressure, is transmitted to the cylinder wall via the water jacket bottom wall from a head bolt boss. Therefore, the cylinder wall may deform and cause scuffing of the cylinder bores, which leads to an increase of oil consumption.